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Introduction to objective c

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Introduction to objective c

  1. 1. Introduction to Objective C
  2. 2. Objective C •  Objective C is a programming language, which is used by Apple for developing the application for iPhone and Mac Systems. •  Objective C is very old programming language and it was designed and developed in 1986. Now Objective C has become popular once again as it is being used by Apple to develop applications for Mac system and iPhone. •  Full superset of C language •  Allows any traditional C code. •  Adds powerful Object oriented capabilities.
  3. 3. OverView •  Objective C consists of objects, classes, instance variables, methods. •  Built entirely around objects. •  Objects like Windows, views, buttons, controllers exchange information with each other, respond to events, pass actions to run a program. •  In C we write .c and .h files, here we write .h and .m files. •  .h are the header files and .m are the source code or implementation files.
  4. 4. Objective C Language •  •  •  •  •  Keywords Message Classes and method declaration Instance Methods and Class Methods Constructors •  User Defined Constructors •  Categories •  Protocols
  5. 5. Keywords Keywords in objective C has a prefix @ appended to them. We will look at the keywords used for different purposes in this section Keyword Definition @interface This is used to declare a class/interface @implementation This is used to define class/category @protocol This is used to declare a protocol
  6. 6. Keywords Cont… Interface The declaration of a class interface begins with the compiler directive @interface and ends with the directive @end. @interface ClassName : ItsSuperclass { instance variable declarations } method declarations @end the name of the interface file usually has the .h extension typical of header files.
  7. 7. Keywords Cont… Implementation The definition of a class is structured very much like its declaration. It begins with the @implementation directive and ends with the @end directive @implementation ClassName : ItsSuperclass method definitions @end The name of the implementation file has the .m extension, indicating that it contains Objective-C source code.
  8. 8. Keywords cont.. Next are the access modifiers. They decide the visibility/ scope of the instance variables/methods Keyword Definition @private The instance variable is accessible only within the class that declares it. @public The instance variable is accessible everywhere @protected The instance variable is accessible within the class that declares it and within classes that inherit it.
  9. 9. Keywords Cont… Other keywords: Keyword Description @class Declares the names of classes defined elsewhere. @”string” Defines a constant NSString object in the current module and initializes the object with the specified string. @property Provides additional information about how the accessor methods are implemented @synthesize Tells the compiler to create the access or method(s)
  10. 10. Keywords Cont… Declaring a simple property @interface MyClass : NSObject { float value; } @property float value; @end A property declaration is equivalent to declaring two accessor methods i.e. -(float)value; -(void)setValue:(float)newValue; These methods are not shown in the code but can be overridden.
  11. 11. Keywords Cont… Synthesizing a property with @synthesize @implementation MyClass : NSObject @synthesize value; @end When a property is synthesized two accessor methods are generated i.e. -(float)value; -(void)setValue:(float)newValue; These methods are not shown in the code but they can be overridden.
  12. 12. Keywords Cont… Self l  Self is a keyword which refers to current class. { [self setOrigin:someX :someY]; } In the example above, it would begin with the class of the object receiving the reposition message.
  13. 13. Keywords Cont… super l  l  It begins in the superclass of the class that defines the method where super appears. Super is a keyword which refers to the parent class. { [super init]; } { [super dealloc]; } In the example above, it would begin with the superclass of the class where reposition is defined.
  14. 14. Message •  It’s the most important extension to C •  Message is sent when one object asks another to perform a specific action. •  Equivalent to procedural call in C •  Simple message call looks like [receiver action], here we are asking the . receiver to perform the action •  Receiver can be a object or any expression that evaluates to an object. •  Action is the name of the method + any arguments passed to it.
  15. 15. Message with Arguments •  Sometimes we pass one or more arguments along with the action to the receiver. •  We add a argument by adding a colon and the argument after the action like [receiver action: argument] •  Real world example of this is [label setText:@”This is my button”]; •  String in Objective C is defined as @””; •  Multiple arguments can be passed to a action like this [receiver withAction1:argument1 withacction2:argument2]; For example: [button setTitle:@”OK” forState:NO];
  16. 16. Classes and Method Declaration •  Class in objective C is a combination of two files ie .h and .m •  .h file contains the interface of the class. •  .m contains the implementation Class Definition .h file .m file @interface @implementation Variable and methods declaration Method definitions
  17. 17. Classes and Method Declaration •  Example of a Person class. •  Here we define the interface and implementation in Person.h and Person.m file respectively Person.h file #import<Foundation/NSObject.h> @interface Person: NSObject { NSString *name; } -(void) setName: (NSString *)str; +(void) printCompanyName; @end
  18. 18. Classes and Method Declaration •  Now the contents of Person.m file •  #import Person.h @implementation Person -(void) setName: (NSString *) str { name=str; } +(void) printCompanyName { printf(“This is class method”); } @end; Here we have defined a Class Person which has a instance variable “name” and a method “setName”.
  19. 19. Classes and Method Declaration •  Using the Person class #import<stdio.h> #import “Person.m" int main() { Person *c = [[Person alloc] init]; // Allocating and initializing Person [c setName : @”Rahul”]; // Setting Name of the allocated person [Person printCompanyName] // calls class method [c release]; // releasing the person object created return 1; // return }
  20. 20. Instance and Class Methods •  In objective C we can define methods at two levels ie Class Level and Instance level •  In previous Example we declared a method with a – sign prefixed. That was a instance level method. •  If we put + instead of – then we get a class level method. •  A instance method can be called by the instances of the class. But a class level can be called without creating any instance. •  Example to call a instance method; Person *p=[[Person alloc] init]; [p setName:@”Sunil”]; •  Example to call class method [Person printCompanyName];
  21. 21. Creating multi parameter method Objective-C enables programmer to use method with multiple parameter. These parameter can be of same type or of different type. MyClass.h MyClass.m #import<Foundation/NSObject.h> #import<stdio.h> #import"MyClass.h" @interface MyClass:NSObject{ } // declare method for more than one parameter -(int) sum: (int) a andb: (int) b andc: (int)c; @end @implementation MyClass -(int) sum: (int) a andb: (int) b andc: (int)c;{ return a+b+c; } @end
  22. 22. Creating multi parameter method Objective-C enables programmer to use method with multiple parameter. These parameter can be of same type or of different type. main.m #import"MyClass.m" int main() { MyClass *class = [[MyClass alloc]init]; NSLog(@"Sum is : %d",[class sum : 5 andb : 6 andc:10]); [class release]; return ; } Output: Sum is: 21
  23. 23. Constructors •  When a class is instantiated a constructor is called which is used to initialize the object properties •  When a constructor is called it returns an object of a class. •  If a user does not provide a constructor for a class the default one is used. •  The default constructor is -(id) init; id is a special keyword in Objective C which can be used to refer to any object. •  Remember in our Person class example while instantiating the Person class we called the constructor. [[Person alloc] init]; It returns a person object.
  24. 24. Categories •  Typically when a programmer wants to extend the functionality of a class, he subclasses it and adds methods to it. •  Categories can be used to add method to a class without subclassing. •  Here’s how you create a category @interface PersonCategory (personcat) @implementation PersonCategory (personcat)
  25. 25. Categories •  •  •  Implementation of category. personcat.h file contains #import “Person.h" @interface Person (personcat) -(void) updateName: (NSString *) str; @end personcat.m file contains #import “personcat.h ” @implementation Person (personcat) -(void) updateName: (int)value{ Printf(“%d”,value); } @end The updateName name method now behaves as if it’s the part of Person Class.
  26. 26. Protocols •  Protocols are like interfaces in Java •  It declares a set of methods, listing their arguments and return types •  Now a class can state that its using a protocol in @interface statements in .h file •  For example @interface Person:NSObject <human> Here human is a protocol. •  Defining a protocol @protocol human <NSObject> -(void) eat; @end
  27. 27. Keywords Cont… •  Memory management keywords Keyword Description Alloc Allocates memory for an object Retain Retains a object Releae Releases memory of an object Auto release Auto release memory used by an object
  28. 28. Memory Management •  In objective C a programmer has to manage memory ie allocate and deallocate memory for objects. •  While instantiating a person object we allocated the memory for the object by this call. Person *p=[[Person alloc] init]; •  We have to release whatever objects we create programatically. Memory management for other objects is taken care of by the Objective C runtime. •  We use release action to release the unused memory. The syntax for this is [p release];
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